(1) Field of the Invention
The present invention relates to devices for processing analog and/or digital signals, and more particularly, to integrated circuits that utilize multiple clock frequencies for digitizing and processing various analog and/or digital signals.
(2) Description of the Related Art
Integrated circuits, or ICs, are extensively used in all types of electronic devices. As these electronic devices become more complex, the number of ICs necessary to perform all of the required functions increases and/or the functions of several ICs are combined into a single IC. Even as multiple functions are consolidated into a single IC, it is desirable to reduce the internal complexity of the IC.
Current televisions use many different ICs for processing both analog and digital television signals from various terrestrial and non-terrestrial sources. The next generation of digital/analog televisions, however, will be expected to have even higher levels of integration than current televisions. Higher levels of integration translate into fewer ICs, wherein processes performed by several individual ICs are combined into one IC. However, various obstacles stand in the way of combining processing from analog television signal receivers with those required for digital television signals.
A problem with respect to integration of analog and digital television signal processing ICs is that different sources of video (both analog and digital) may require analog-to-digital (A/D) converters to be run at different sampling rates. Analog television signals are based on line-locked or chroma sub-carrier-locked frequencies, while digitally modulated (digital) television signals are based on their own symbol rates. Also, present A/D technology produces digital crosstalk that adversely affects A/D performance when asynchronous clocks are present.
It is known to use stand-alone digital demodulators using digital interpolation for off-frequency operation. Also, second channel processing for analog signals has been accomplished with an asynchronous sample frequency. In the latter case, however, the main channel is locked to a parameter of the incoming analog television signal, such as horizontal sync pulses or color burst.